将字符串传递给filter（dplyr）的参数

Question

let's say I have a list of conditions:

input_list <- list(Species = "setosa",
                   Petal.Width = 0.2)

I can turn this list into a string:

x <- map(input_list, ~ paste0( " == ", "'", .[[1]], "'"))
conditions <- paste(names(x), x, collapse = ", ")


conditions
> [1] "Species  == 'setosa', Petal.Width  == '0.2'"

I would like to pass this string as conditions to filter :

iris %>% filter(rlang::sym(conditions))

But unfortunately I get an error

Error in filter_impl(.data, quo) : Argument 2 filter condition does not evaluate to a logical vector

Answer 1

You can try collapsing your conditions into a string of form cond1 & cond2 and use eval(parse(text=...))

input_list <- list(Species = "setosa",
                   Petal.Width = 0.2)

x <- map(input_list, ~ paste0( " == ", "'", .[[1]], "'"))
conditions <- paste(names(x), x, collapse = " & ")
conditions
# [1] "Species  == 'setosa' & Petal.Width  == '0.2'"

iris %>% filter(eval(parse(text = conditions)))
   # Sepal.Length Sepal.Width Petal.Length Petal.Width Species
# 1           5.1         3.5          1.4         0.2  setosa
# 2           4.9         3.0          1.4         0.2  setosa
# 3           4.7         3.2          1.3         0.2  setosa
# 4           4.6         3.1          1.5         0.2  setosa
# 5           5.0         3.6          1.4         0.2  setosa
# 6           5.0         3.4          1.5         0.2  setosa
# 7           4.4         2.9          1.4         0.2  setosa
# 8           5.4         3.7          1.5         0.2  setosa
# 9           4.8         3.4          1.6         0.2  setosa
# etc

But I prefer Frank's answer in comment

Answer 2

filter_ would do the job instead of filter

conds <- stringr::str_split(conditions, ", ")
iris %>% filter_(conds[[1]][1], conds[[1]][2])

Update following up your comment:

You can loop through the conditions which would work regardless of length:

for(i in conds[[1]]) {
  iris <- iris %>% filter_(i)
}